Nomorhamphus is a genus of halfbeaks — surface-dwelling fish named for the elongated lower jaw that projects well past a short upper one — endemic to the freshwaters of Sulawesi and the Philippines. What sets the genus apart from most other halfbeaks, which scatter eggs, is that Nomorhamphus are livebearers: females retain fertilised eggs internally and give birth to free-swimming young, a trait shared with only a few halfbeak lineages worldwide. They favour fast-flowing forest streams, sit near the surface picking off insects that fall onto the water, and males of many species develop an andropodium — a modified, asymmetrical anal fin used to transfer sperm internally — along with enlarged jaws used in courtship sparring between rivals.
The best-known aquarium representative is N. liemi, the Celebes halfbeak, kept by livebearer specialists for its unusual biology and the males' territorial sparring, though the group as a whole stays a niche interest rather than a mainstream one. Conservation status is a real concern here: of the 22 species in the atlas, four are listed Endangered and four more Near Threatened, against Sulawesi's endemic-rich but heavily pressured river systems, and one species carries an active CARES breeding-priority listing on the atlas — a rare distinction among the world's halfbeaks.